WENDY HARRIS, senior pharmacist, safe medication practice, primary care, National Patient Safety Agency, replies:

The article mentioned by Mrs Stewart refers to patients treated in a community setting in England. To clarify, this refers to the context in which patients receive their treatment, ie, via prescription but taken in their own homes. The data cover the whole of the UK and relate to a 10-year period from 1993 to 2002, during which time more than 500,000 prescriptions were issued for oral methotrexate within primary care. Additionally, some patients received medicines supplied through secondary care via specialist clinics which were subsequently also administered in the community setting. It is important to emphasise that oral methotrexate is a safe and effective medicine if taken at the right frequency, in the right dose and with the appropriate monitoring.

Approximately 50,000 prescriptions are issued per year in primary care, although it is not possible to ascertain how many patients receive methotrexate at any one time. The NPSA work has been informed by data drawn from a wide range of sources.

In relation to the final question on what proportion of the 25 patient deaths and 26 cases of serious harm occurring over the 10-year period were the result of human error, it is not possible for us to identify which cases were caused as a direct result of human error because most of the data were not collected by the NPSA (which was established in July 2001) and individual cases have therefore not been subject to a root cause analysis by us. We do know from our work on other aspects of medication error that the causes of error are numerous, and although human error might be identified as key at a superficial level, the underlying common factors, themes and patterns have shown that a significant majority are systems- or process- induced. For example, prescribing and dispensing IT systems do not have a default mechanism that allows weekly dosing which can lead to patient safety incidents. Since these are complex issues, we are working on a range of solutions to address them.